Computer-aided diagnosis system and method

ABSTRACT

An x-ray system acquires an initial low-contrast, wide latitude (G=2.5, or G=2 or less) x-ray image of a breast. A processing system automatically finds suspected abnormalities in the breast by processing the low contrast initial image, and then automatically converts the initial x-ray image to a high-contrast, narrow latitude image at the locations of the found abnormalities to thereby facilitate diagnosis and patient care. The technology includes effective ways to produce, process and display the various images, and can be extended to other types of images.

REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of parent applicationSer. No. 08/890,254 filed on Nov. 28, 1997 (to be abandoned as of thefiling date accorded to this application). Ser. No. 08/890,254 is inturn is a continuation-in-part of copending parent applications Ser.Nos. 08/579,802 filed on Dec. 28, 1995 (now U.S. Pat. Nos. 5,828,774)and 08/438,432 filed on May 10, 1995 (now U.S. Pat. No. 5,729,620). Inturn, Ser. No. 08/579,802 is a continuation, and Ser. No. 08/438,432 isa continuation-in-part, of parent application Ser. No. 08/129,255 filedon Sep. 29, 1993 (abandoned). This application hereby incorporates byreference the entire disclosure, drawings and claims of each of saidparent applications as though fully set forth herein.

FIELD, BACKGROUND, AND SUMMARY OF THE DISCLOSURE

[0002] This patent specification relates to displaying radiologicalimages and other information in a manner believed to assist users suchas physicians in reading such images and other information. Morespecifically, it relates to a computer-aided diagnosis “CAD”) system andmethod for detection and identification of abnormalities in radiologicalimages, and to using the results to produce images that provide moreuseful diagnostic information and better patient care. The images can beviewed in conventional format but in conjunction with viewing anannotated road map of the location and/or the identification ofsuspected abnormalities found through computer processing ofradiological images. The annotated map highlights and/or identifiessuspected abnormalities to help the image reader better assess thepresence and/or meaning and significance of abnormalities in theradiological image.

[0003] The utility of the system and method is further improved byinitially acquiring an x-ray image that is low-contrast butwide-latitude (G=2.5, or G=2 or less). In the case of breast imaging, alow-contrast, wide latitude x-ray image makes it possible to include inthe image significant information about both very dense and much lessdense tissue whereas normal x-ray film (typically G=3) may not recordsufficient information about dense breast tissue. On the other hand, alow-contrast image may not be as suitable for viewing, and laws andregulations may prohibit the use of film of G less than 3 for breastdiagnosis. In a preferred embodiment, the low-contrast image isautomatically processed in the electronic domain to find suspectedabnormalities, taking advantage of the fact that the wide latitude mayallows the film to contain more information than conventional images.Resulting information regarding such abnormalities is in turn used as aguide in automatically converting the initial, low contrast image to adisplay image that is high-contrast at areas of the suspectedabnormalities, to thereby facilitate diagnosis and patient care.

[0004] The detection of abnormal anatomic regions in radiological imagesusing a computer system comprising specialized software and possiblyspecialized hardware has been reported. For example, in the area ofmammography, representative reports are: Giger et al in the May 1993issue of RadioGraphics, pages 647-656; Giger et al in Proceedings ofSPIE, Volume 1445 (1991), pages 101-103; Doi et al in U.S. Pat. No.4,907,156; and Giger et al in U.S. Pat. No. 5,133,020. See, also, thedisclosure of and in prior art cited in said parent applications. Inparticular, in the area of detecting spiculated or stellate lesions inmammograms using convergent line detectors as the principal abnormalfeature detection algorithm, representative reports are: N. Karssemeijerin the book entitled “Digital Mammography”, edited by A. G. Gale et al,published by Elsevier in 1994, pages 211-219; and Kegelmeyer et al inVolume 191 (1994) of Radiology, pages 331-337. In the area of detectingclusters of microcalcifications in mammograms using thresholding and aclustering kernel as the principal abnormal feature detection algorithm,representative report are: Nishikawa et al in Volume 20 (1993) ofMedical Physics, pages 1661-1666; and Feig et al in Volume 33 (1995) ofRadiological Clinics of North America, pages 1205-30. See, also,co-pending patent applications Ser. No. 08/676,660 filed on Jul. 10,1966 entitled “Method and apparatus for fast detection of spiculatedlesions in digital mammograms,” and Ser. No. 08/901,541 filed on Jul.28, 1997 entitled “Method and system for using local attenuation in thedetection of abnormalities in digitized medical images.” These twopatent applications and each of the other references cited in thispatent specification are incorporated herein by reference as thoughfully set forth herein. These systems are generally referred to asComputer-Aided Diagnosis (“CAD”) systems, and are believed to beparticularly useful to radiologists in the diagnostic process andparticularly in screening radiological procedures. R2 Technology, Inc.of Los Altos, Calif. offers technology under the trade name ImageCheckerand a system under the trade name ImageChecker M 1000 to assistphysicians in their review of screening mammograms by identifying imageareas that might require further review. Information on this technologyis available at www.r2tech.com.

[0005] In a screening radiological procedure, such as screeningmammography, the patients typically are asymptomatic and trueabnormalities (e.g. cancers) are said to occur at a typical rate ofabout one case per one hundred patient examinations. Reading of themammograms, when most of them are negative, can be a tedious task thatcan make it difficult to maintain a constantly high attention level.Some detectable abnormalities can be missed or misdiagnosed, which canresult in delayed or more costly treatment, and can even result in areduction of patient's longevity or chance of survival. According to anarticle in the May 26, 1993 issue of JAMA, pages 2616-2617, themisdiagnosis rate in mammograms can be in the range of 15 to 63%. TheCAD system, serving as an electronic reminder or second reader, as aspell-checker can be in a word processor, can assist radiologists inattaining higher detection rate (higher sensitivity) for abnormalitiesor reducing the misdiagnosis rate (lowering the false-negative rate).

[0006] Applicant understands that a current procedure using a CADmammographic system proceeds as follows. The physician views aradiological image, reaches a preliminary diagnostic decision, and thenviews a separate second image displayed on a CAD system. This secondimage is marked or annotated with a localized identification of theabnormalities that the CAD system has detected through computer analysisof a digitized version of the conventionally obtained radiologicalimage. After a reexamination the area of the radiological image thatcorresponds to the position of the detected abnormalities displayed onthe CAD system, the physician makes the final diagnostic decision. Thisfinal diagnostic decision may or may not be the same as the preliminarydecision, depending on whether the physician found the additionaldiagnostic information provided by the CAD system to be significant and,if so, what significance the physician ascribed to it. Following thefinal diagnostic decision, and perhaps depending on the degree ofsuspicion for malignancy, the physician can recommend a course offurther action, which can include no further action or further follow-upexaminations or biopsy.

[0007] In the process of detecting abnormal anatomic features inradiological images using a CAD system as described in the above citedreferences, the radiological film image of a patient is processedthrough a film digitizer to generate a digitized image which is input assuch into the system. The digitized image is then analyzed by a digitalimage processing computer with specialized software and perhaps alsospecialized hardware for abnormal anatomic feature detection. Ifabnormalities are detected, an annotated radiological image is displayedon a special TV monitor, with markers placed around or adjacent thedetected abnormalities. This TV monitor typically has a large dimension(typically a screen diagonal of 12 inches or larger) and a high spatialresolution (typically more than 1000×1000 pixels). Because of the largedimension and high spatial resolution, this TV monitor typically ispositioned at some distance away from the film. Typically the center ofthe monitor is more than 12 inches from the center of the film on theconventional film illumination box. In addition, this special TV monitortypically has a low brightness and a high cost.

[0008] It is believed that the display method using a high-resolution TVmonitor has certain shortcomings that make the process inconvenient andinefficient. The high-resolution TV monitor is expensive, its spatialresolution although high for monitors is still less than that of theoriginal x-ray film, and its brightness and dynamic range are alsoinferior to those of an x-ray film viewed on a light box. Therefore, itis believed that a physician might not wish to rely solely on the imagedisplayed on the TV monitor to make diagnosis, but typically wouldrepeatedly go back to the conventional film illumination box to view theoriginal film image. This can lead to the loss of valuable time and canbe uncomfortable at least because of the different brightness levels andspatial resolution levels of the two images. In addition, it is believedthat diagnostic errors can arise from the need for the physician toshuttle back and forth between two different displayed images. Even whena potentially true abnormality (cancer) is detected and pointed out bythe CAD system to the physician, the fatigue and eye discomfort andother effects due to viewing two images of such differentcharacteristics may still cause the physician to miss the significanceof the corresponding area on the original x-ray film and to fail tonotice or appreciate the abnormal features of the detected abnormalityand decide to ignore the detected abnormality.

[0009] Accordingly, one object of this patent specification is toprovide an improved combined display of an x-ray radiological image andCAD-detected abnormalities from the x-ray image. A more specific objectis to provide the CAD user with further processed, annotated andenhanced image representations of regions around the CAD detectedabnormalities in order to emphasize abnormal image features of thesedetected abnormalities. Another more specific object is to produce aninitial image that is low-contrast but wide latitude and use it toautomatically find suspected abnormalities, and use information aboutthe suspected abnormalities to automatically convert the initial imageto a display image that is high-contrast at the density range of thefound abnormalities. The ultimate goal is to help the user (physician)better assess the type and degree of abnormality of these detectedabnormalities in the radiological image.

[0010] Another objective is to present the further processed image ofthe area around the CAD detected abnormalities on a display such as asmall TV monitor located close to the x-ray film during viewing of thex-ray film. The term TV monitor is used generically, to refer to anytype of electronic display, for example a flat panel display. The twoimages should be so close and should otherwise match each other suchthat eye and other discomfort due to viewing two different imagesalternately would be reduced. Still another object is to print theannotated road map and/or the further processed image representations ofareas around the CAD detected abnormalities on the same sheet ofphotographic film that contains a printout of the radiological image.

[0011] This patent specification describes in detail, toward the end,the preferred embodiment that derives a low-contrast, wide latitudeimage, automatically extracts information about suspected abnormalitiestherefrom, and uses that information to automatically produce a displayimage that is high-contrast at the areas of the suspected abnormalities.Earlier parts of the patent specification describe embodiments involvingprimarily various ways to obtain an x-ray image, extract informationregarding suspected abnormalities, and display that information in waysthat facilitate diagnosis and treatment.

[0012] In an exemplary and non-limiting first embodiment, the furtherprocessed image of areas around the CAD detected abnormalities from aradiological film is presented on a small TV monitor, located in closeproximity to the radiological film being viewed at the light box. Thedisplay of this further processed image shares (e.g., is toggled on) thesmall TV monitor with the display of a miniaturized annotated road map.On demand by the CAD user, e.g. the physician using a toggle switch, theminiaturized annotated road map image and the further processed imagerepresentations such as tiles of areas around the CAD detectedabnormalities are displayed alternatively on the small TV.

[0013] In an exemplary and non-limiting second embodiment, theminiaturized annotated road map image is presented on a small TV monitorand further processed image tiles of areas around the CAD detectedabnormalities are presented on a second and separate small TV monitor.Both small monitors preferably are located in close proximity to theradiological film being viewed at the light box.

[0014] In an exemplary and non-limiting third embodiment, theradiological image is acquired through digital means, and thus is indigital form initially. The radiological image can be displayed as anelectronic image on a high-resolution monitor. The annotated map and, ifdesired the tiles as well, can be displayed on the same monitor, at anarea that does not overlap with the areas of interest of the displayedradiological image. In some cases, the digitally acquired radiologicalimage is printed on a sheet of photographic film for later viewing on alight box. In that case, the annotation road map and, if desired thetiles as well, can be printed on the same sheet of photographic film, atan area that does not obscure relevant parts of the radiological image.

[0015] In an exemplary and non-limiting fourth embodiment, a CAD systemis used to enhance the informational content of image displays, bytaking an initial radiographic image that has a low contrast but widelatitude. This allows imaging well on the same film or other imagingsystem of tissues that differ greatly in density. The initial image isprocessed to identify area of possible interest, such as areas ofsuspected abnormalities. Based on characteristics of these areas, theinitial image is converted to a display image that has high contrast atthe density range(s) of the already identified areas of possibleinterest and thus can provide enhanced diagnostic information and assistin any further treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram illustrating a CAD system and its outputdisplay according to a first embodiment.

[0017]FIG. 2 is a block diagram illustrating a CAD system and its outputdisplay according to a second embodiment.

[0018]FIG. 3 is a block diagram illustrating a CAD system and a firstmethod of output display according to the third embodiment.

[0019]FIG. 4 is a block diagram illustrating a CAD system and a secondmethod of output display according to the third embodiment

[0020]FIG. 5 is a block diagram illustrating a CAD system and an outputdisplay according to a fourth embodiment.

[0021]FIG. 6 illustrates displaying an output according to the fourthembodiment.

[0022]FIG. 7 compares film characteristics of wide latitude films usedin the fourth embodiment with characteristics of the prior art film.

DETAILED DESCRIPTION

[0023] Referring to FIG. 1, a preferred but non-limiting example of afirst embodiment generates an annotated road map of CAD-detectedabnormalities and a further processed image of the area around the CADdetected abnormalities from a radiological film. The annotated road mapand/or the further processed image are displayed on one or more small TVmonitors located in close proximity to the radiological film beingviewed at a light box. In this example, the radiological film is in theform of a mammographic x-ray film acquired with a conventionalmammographic film-screen imaging system. The original analogtwo-dimensional mammographic x-ray film 10, with a patient informationlabel 12 printed at an edge of the film, is sent through a filmdigitizer 30 of a CAD (computer-aided diagnosis) system 20. This system20 can be the system disclosed in the U.S. patent applicationsincorporated by reference herein, and generates a digitizedtwo-dimensional mammographic image 40. Preferably, the film digitizer 30should be a laser film digitizer or a high performance CCD based filmdigitizer and should have a dynamic range and a spatial resolutioncomparable to those of the original mammographic film. Such filmtypically has a dynamic range of 10,000:1 and spatial resolution ofapproximately 50 microns per pixel (or about 4,000×5,000 pixels for8-inch×10-inch film. The identity of the original mammographic image 10is entered into the CAD system at this point to identify the digitizedmammographic image 40 and thus the original film 10. An useful option atthis point is to automatically input the identity of the originalmammographic image 10 into the CAD machine. This can be accomplished inmany ways—for example, by labeling the mammographic film 10 with a codesuch as a bar code close to the a patient information label 12 printedon the edge of the film, or by incorporating the bar code into thepatient information label 12. The label can then be read into the CADsystem 20 with an optional ID bar code reader 15 as the mammographicfilm 10 is being fed into the film digitizer 30.

[0024] The digitized mammographic image 40 is then sent through anabnormal feature detection stage 50 of the CAD system, or CAD machine,20. The findings or results, positive or negative in nature, from theabnormal feature detection stage 50 typically are in the form of atwo-dimensional annotation map 55. The map identifies the locations andtypes of the CAD-detected abnormalities 56 and 57 (in this illustrativeexample) present in the original film image 10. For the purposes of anillustration, let the abnormality 56 be a spiculated lesion and lei, itslocation on the annotated map be marked with a star-shaped marker. Letthe abnormality 57 be a cluster of microcalcifications and let itslocation on the annotated map be marked with a triangular shaped marker.Thus, the markers identify not only the detected location but also thedetected nature of the suspected abnormality identified at this stage.The annotation map 55 can be scaled down to a sub-sampled image, say512×512 pixel in size and 8-bit in gray scale, as the digitized image40. The two superimposed images, 55 and 40, in registration with eachother, form a miniaturized annotated road map image 58. Enhanced imageareas or tiles 66 and 67 are centered around the CAD-detectedabnormalities 56 and 57, respectively, and can be, for example, 512×512pixel in size and 8-bit in gray scale. They are generated by furtherimage processing the regions in the digitized image 40 which correspondto the CAD detected abnormalities 56 and 57. The CAD-generatedannotation map 55, the miniaturized annotated road map image 58, theenhanced image tiles 66 and 67, together with the digitized image 40 andits corresponding identification, can be stored for later use in anoptional memory storage unit 70.

[0025] The annotation road map 58 and the enhanced image tiles 66 and 67are transferred to an output display section of the system for display.The output display section of the CAD system can be a part of the totalCAD system, in which case the data transfer can be through a dedicatedshielded cable. Or, the output display section can be a separate system,in which case additional data storage memory can be added to the unit tostore the transferred interim data, and the data transfer can be througha dedicated shielded cable or an existing network where the equipment isinstalled.

[0026] It is important to point out and emphasize the abnormal featuresof the CAD detected abnormalities to the physician. The reason is thatthe physician, even after seeing the location of the CAD detectedabnormalities on the miniature road map 58, may still fail to notice orappreciate corresponding abnormal features on the original the x-rayfilm. By pointing these abnormal features out, with further emphasis, tothe physician, it is believed that the physician would be in betterposition to assess the level and nature of abnormality of these CADdetected abnormalities. The principal abnormal feature detectionalgorithms used in the abnormal feature detection stage 50 to detect theabnormalities can be used to further emphasize the abnormal features ofthe CAD detected abnormalities. For example, in the case of theabnormality 56, the principal abnormal feature used to detect thespiculated lesion can be a set of convergent lines. Since the presenceof the convergent lines around a lesion raises the probability ofmalignancy, it is believed that there would be less a chance that thephysician could ignore the lesion if the convergent lines were made morenoticeable. Therefore, this set of convergent lines around thespiculated lesion could be contrast and edge enhanced to form the imagetile 66. For example,

[0027]FIG. 3(B) of Karssemeijer article cited shows a set of detectedpixels pointing to the center of a suspected spiculated lesion.Superimposing these detected pixels on the image can form the image tile66. In the case of the abnormality 57, the principal abnormal featureused to detect the cluster of microcalcifications can be the smallclustering of three or more high contrast spots. This small clusteringof high contrast spots can be enhanced in brightness to form the imagetile 67. The formation of this small clustering of bright spots can beof great interest to the physician. This is because the probability ofmalignancy is higher for a linear or branching formation. Therefore,this small clustering of high contrast spots can also be magnified insize, for example by a factor of 2 or more, to form the image tile 67 inorder to help the physician see the formation of these bright spotsclearly in the image tile 67. In this manner, it is believed that theCAD user, the physician, after seeing the enhanced abnormal imagefeatures of these detected abnormalities and reexamining the originalx-ray image, can better assess the level of abnormality of thesedetected abnormalities in the x-ray image.

[0028] Also shown in FIG. 1 is an illustration of a CAD output displayconsisting of a conventional film illuminator, commonly called a lightbox, 100 and a small TV monitor 200 according to the first embodiment.In this exemplary embodiment, the miniaturized annotated road map 58 andthe enhanced image tiles 66 and 67 are alternatively or sequentiallydisplayed as images 300 x, by operating a toggle switch 90 to displayone image at a time (where x=a, b and c) on the small TV monitor 200located in close proximity to the original film 10. Respectively, theimage 300 a represents the miniaturized annotated road map 58, the image300 b represents the enhanced image tile 66 around the CAD detectedspiculated lesion, and the image 300 c represents the enhanced imagetile 67 around the CAD detected cluster of microcalcifications. If moreabnormalities were detected, there would be images 300 d, 300 c, etc. tobe toggled through the small TV monitor.

[0029] The dimensions of the display screen of the small TV monitor 200in this example preferably, but not necessarily, are of the order of ¼to ½ of the dimensions of original film 10. In addition, the small TVmonitor 200 should preferably be located as close as practical to thelight box 100 displaying the original film 10. Preferably the center ofthe small TV monitor 200 should be less than 12 inches from the centerof the original film 10 on the conventional film illumination light box100. The preferred position, as shown in FIG. 1, for mounting the smallTV monitor 200 is just beneath the light box 100 that displays theoriginal image 10. It is also convenient to display a pair of images oneach TV monitor, since frequently a pair of the original mammographicfilms 10, such as the mammograms of the left and right breasts, aredisplayed and viewed next to each other. In this manner, the physicianstill has to minimally move his or her eyes back and forth between theoriginal radiological film image 10 on the film illuminator 100 and theimages 300 x displayed on the small TV monitor 200. The spatialresolution of the small TV monitor 200 can be in the range of 500 TVlines, or comparable to that of NTSC or PAL. The brightness level of thesmall TV monitor 200 should be similar to that of the average brightnesstransmitted through the original film 10, so that the observer would notbe bothered by a change in brightness. In using the CAD system as asecond reader in a screening situation, it is sometimes preferred thatthe display on the small TV monitor 200 can be easily toggled withon-off with a switch 90 by the observer. As a variation, more than onemonitor 200 can be used; for example, one can display the annotated map58 and at least one other monitor can display one or more of the tiles.The tiles can be displayed on a single monitor, by toggling from one toanother, or each of two or more tiles can be displayed at a respectivemonitor. The one or more monitors can be placed at positions relative tothe light box other than those illustrated in FIG. 1

[0030]FIG. 2 is similar to FIG. 1 in many respects, and similarlylabeled components serve a similar function and therefore will not bedescribed again in detail. FIG. 2 shows a CAD output display comprisinga conventional film illuminator 100 and, in this case, two small TVmonitors 200 and 250, according to a second embodiment. In thisexemplary embodiment, the annotated information 58 is presented as aminiaturized annotated road map image 300 a on the first small TVmonitor 200, located in close proximity to the original film 10. Theenhanced image tiles 66 and 67 are alternatively or sequentiallypresented, by operating a toggle switch 90, as images 300 b and 300 c onthe second small TV monitor 250, located next to the first small TVmonitor 200 and in close proximity to the original film 10. It issometimes preferred that two or more small TV monitors are used, inplace of monitor 250, to display the further processed image tiles 66and 67 such that each detected abnormality is displayed on a separatesmall TV monitor at the same time. The small TV monitors 200 and 250 canbe placed at other positions relative to the light box 100, e.g. to theside or above light box 100. More than one monitor can be used todisplay the tiles.

[0031] Referring to FIG. 3, a preferred but non-limiting exampleaccording to a third embodiment receives radiological images whichalready are in the digital format, detects abnormalities on theseradiological images with a CAD system, and prints out the radiologicalimages together with CAD results on photographic film. Again, componentslabeled the same as in FIGS. 1 and 2 serve similar functions andtherefore will not be described again in detail. Digital imaging systemsthat provide images in digital form include but are not limited tomagnetic resonance imaging (“MRI”) systems, computed tomography (“CT”)systems, ultrasound imaging systems, scintillation cameras, computedradiography (“CR”) systems (such as Fuji's CR system based on stimulatedemission phosphor detector), and recently reported and introduceddigital radiography and digital mammography systems (for example, seeFeig article cited earlier; using CCDs or amorphous silicon arraydetectors), and recently popular digital mammography and other x-raysystems using flat panel x-ray detectors. In this example, theradiological image is in the form of a digital mammogram, which isacquired with a digital mammography system. This digital mammogram 14,already having properly encoded identification and patient information12, is reformatted into the digitized mammographic image 40 and is sentthrough the abnormal feature detection stage 50 of the CAD machine 20.If the information is already properly formatted for the CAD machine 20,it is sent directly to and through the abnormal feature detection stage50 of the CAD machine 20 without reformatting. The initial filmdigitization step used in the first and second embodiments for analogmammograms is not needed in this case. As in the first and secondembodiments, the findings or results, positive or negative in nature,from the abnormal feature detection stage 50 are in the form of atwo-dimensional annotation map 55 showing the locations and types of theCAD-detected abnormalities 56 and 57. For the purposes of anillustration, let the abnormality 56 be a spiculated lesion and let itslocation on the annotated map be marked by a star shaped marker. Let theabnormality 57 be a cluster of microcalcifications and let its locationon the annotated map be marked by a triangular shaped marker. Theannotation map 55 can be scaled down to the same size of a sub-sampledimage, say 512×512 pixel in size and 8-bit in gray scale, of thedigitized image 40, and the two superimposed images in registration witheach other form a miniaturized annotated road map image 58. Enhancedimage tiles 66 and 67, centered respectively around the CAD-detectedabnormalities 56 and 57, say 512×512 pixel in size and 8-bit in grayscale, are generated by further image processing the regions in thedigitized image 40 which correspond to the CAD detected abnormalities 56and 57. The CAD-generated annotation map 55, the miniaturized annotatedroad map image 58, the enhanced image tiles 66 and 67, and together withthe digitized image 40 and its corresponding identification, can bestored for later use in an optional memory storage unit 70.

[0032] The annotation road map 58 and the enhanced image tiles 66 and 67are transferred to the output display section of the system for display.There are several methods to display the CAD results and the digitallyacquired mammogram. Since the digital system produces no film to startwith at the acquisition, the first method is a totally filmless displayby using a high resolution TV monitor 400. The resolution should be atleast 1000×1000 pixels. In this method the annotation road map 58, theenhanced image tiles 66 and 67, and the digital mammogram 40 are alldisplayed on the same TV monitor as a combined digital image 450 asshown in FIG. 3. The annotation road map 58 and the enhanced image tiles66 and 67 are shown placed at the edge or margin of the combined digitalimage 450. Patient information 12 can also be displayed at the same edgeor margin of the combined digital image 450. The annotation road map 58may alternatively be displayed by overlaying it on top of the digitalmammogram 40. This overlay may be toggled (switch not shown) on and offso that the digital mammogram 40 can be examined without obstruction.The enhanced image tiles 66 and 67 can also be toggled (switch notshown) on and off. Alternatively, the map and tiles can be displayed onone or more monitors as in the previously disclosed embodiments.

[0033] The second method of display, shown in FIG. 4, where the samereference numerals have the same significance as in the earlier Figures,makes a photographic film printout of the digital mammogram 40, theminiaturized annotation road map 58 and the enhanced image tiles 66 and67 all on a same sheet of film 500. The printout film 500 is viewed on alight box 550. Since, at the present time, physicians usually are moreaccustomed to a photographic film, which typically conveys informationwith higher spatial and contrast resolution and gray scale range than ahigh resolution TV monitor, the second method of display can bepreferred over the first method. The annotation road map 58 and theenhanced image tiles 66 and 67 are shown in FIG. 4 placed at the sameedge or margin of the printout film as the patient information label 12.The photographic film printout, typically having a resolution of4000×5000 pixels, can be made with a high resolution laser film printer580. Such high resolution, 4000×5000 pixels, laser film printers arecommercially available with a resolution of 40 microns per pixel for 8inch×10 inch size films and 100 microns per pixel for 14 inch×17 inchsize films. It is sometimes preferred that only the miniaturizedannotation road map 58 be printed at the edge of the printout film 500.Alternatively, monitors can be used to display the annotated map and thetiles as in the preceding embodiments.

[0034] Digital radiological images, such as, without limitation, in thecase of images from magnetic resonance imaging (“MRI”), computedtomography (“CT”), digital fluorography (“DF”), and computed radiography(“CR”), are sometimes printed out on sheets of 4000×5000 pixelsphotographic film for later viewing on a light box. Since MRI images aretypically formatted into 256×256 pixels, CT images into 512×512 pixels,DF images into 1024×1024 pixels, and CR images into 2048×2048 pixels,many images from MRI or CT or CR modalities can be printed as smalltiles in an array on one sheet of 4000×5000 pixels photographic film.Therefore, the CAD findings from these images can be printed as one orseveral of the tiles. A further refinement on the use of CAD is toreduce the number of images to be presented to the physician, forexample by not presenting radiological images on which no suspectedabnormalities are found by the CAD system, or by not presenting suchradiological images for a second opinion or review by anotherprofessional.

[0035] Although the embodiments discussed above have been described interms of preferred structures involving a single sheet of film, itshould be apparent to those skilled in the art that this patentdisclosure applies to viewing of multiple films on a multiple-filmviewing station or an alternator (a multiple film viewer havingpre-loaded films and a transport belt), to allow several x-ray films 10or printout films 500 to be viewed at the same time or different times,with or without their respective annotation maps 58 and the enhancedimage tiles 66 and 67.

[0036]FIG. 5 illustrates a system in accordance with a fourthembodiment. In this example, an initial radiographic image is alow-contrast but high-latitude film image. Again, the same referencenumerals have the same meanings as in the earlier Figures. The FIG. 5system comprises an analog film-screen acquisition system and a CADsystem similar to the first and second embodiments. However, in thefourth embodiment, the radiological image is acquired on a low-contrastbut wide-latitude mammographic film 600. This embodiment and the thirdembodiment differ in the source of the digitized image 40. Theacquisition system, in this example, uses a relatively inexpensiveconventional mammographic intensifying screen cassette 620. The costratio between this screen cassette 620 and a typical current digitalmammographic system can be several orders of magnitude, e.g.,approximately 1000 times. The standard screen-film acquisition andexposure technique and the conventional mammographic x-ray system (notshown here) will be unchanged for use in this embodiment. The highvoltage of the x-ray generator typically is in the range of 25 to 35 KVp(kilovolt peak) or, as discussed below, can be raised to a level in the40 to 55 KVp range. By reducing the average contrast gradient G of themammographic film 600 say from about 3.0 to about 2.0, or to 1.5 or evenless, we pick up substantial gain in exposure latitude.

[0037] This concept of “wide latitude” is illustrated in FIG. 7, wherethe optical density of the film is plotted against the base 10 logarithmof the x-ray exposure (logE). The latitude is defined as the usablerange of x-ray exposure, which is often expressed as the width in LogE.The conventional “prior art” mammography film is represented by thecurve 702 in FIG. 7. The prior art film is shown to have a latitude ofabout 25 (a width of 1.4 in logE), a maximum optical density ofapproximately 4.2, and an average G of approximately 3.0 (maximum usableoptical density divided by the width in LogE). Two examples in the rangeof the “wide latitude” films used in this preferred embodiment arerepresented by the curves 704 and 706. The 704 film has a latitude ofabout 125 (a width of 2.1 in logE), a maximum optical density (similarto the prior art film) of approximately 4.2, and an average G ofapproximately 2.0 (in this example, 4.2/2.1=2.1). The 706 film has alatitude of about 625 (a width of 2.8 in logE), a maximum opticaldensity of 4.2, and an average G of approximately 1.5 (4.2/2.8=1.5).These are only examples, and it should be understood that thisembodiment can use films of different G ratings that are substantiallybelow 3. Preferably, the G rating of the film is 2.5 or below. Morepreferably, it is 2 or below. G ratings that are 1.5 and below also canbe used in this embodiments.

[0038] Applicant believes that physicians may not use mammography filmsthat have an average G rating below 3 for diagnostic viewing inmammography screening in this country. This is so because applicantunderstands the Congress of the United States passed a law entitled“Mammography Quality Standards Act (“MQSA”) in 1992 to establishnational quality standards for mammography. Mammography films withaverage G of less than 3 would not be able to pass the quality tests,which require the visualization of certain low contrast objects on astandard test phantom. Thus, the low-contrast but high latitude films ofthis embodiment are not intended for use directly for diagnostic viewingby the physician without the additional image processing describedbelow.

[0039] The low-contrast, wide-latitude films can be produced in severalways. One way is to start with a film manufactured such that it isinherently a low-contrast, wide-latitude x-ray film and use aconventional x-ray mammograph with conventional settings to take anx-ray image. Another way is to use the same prior art film with a Grating of about 3, but to process the exposed film at a much lowertemperature than conventional so that the contrast is purposely loweredto correspond to the lower G ratings discussed above. However, thisapproach may not be desired in at least some circumstances because thefilm would not be processed in the manner for which it was designed andconventional processing procedures would have to be changed. Stillanother way is to again use the same prior art film having a G rating ofabout 3, but to raise the x-ray generator high voltage substantially,say to the range of 40 to 55 KVp. The contrast of the breast is thussubstantially reduced, achieving an x-ray image similar to that producedwith a film having the lower G ratings discussed above. This approachhas the added benefit of improved penetration of dense breast, whichpresently can accounts for about 40% of the screening population. Thelower contrast in the breast image can be recovered by subsequent imageprocessing because the better x-ray penetration also brings quantumstatistics.

[0040] Referring again to FIG. 5, because of the low contrast (low G)effects deliberately achieved as discussed above, physicians would notbe expected to make diagnosis by viewing this low contrast and widelatitude mammogram 600. The low-contrast mammographic film 600 isdigitized through the film digitizer 30 and is thereby converted into adigitized image 40 that can be put through the CAD abnormal featuredetection stage 50. This detection can be optimized for use withlow-contrast, wide-latitude images. The result, as in earlierembodiments, is an annotated map 58 of suspected abnormalities, but inthis case derived from the low-contrast image and, if desired, tiles 66and 67. The information generated up to this point can be stored at unit70. Depending on the setting of a switch 71, the information can be usedin one of two ways. One involved displaying the low-contrastradiographic image together with the annotated map and, if desired, thetiles. To this end, the low-contrast but wide latitude image is fedthrough a high-resolution film printer 580 and printed out as aconventional high contrast mammogram 650. The respective annotated roadmaps 58 and the enhanced image tiles 66 and 67 can also be printed atthe edge or margin of the mammogram 650. The physician, as in earlierembodiments, finally reads the mammogram on the light box 550. Using theminiaturized road map 58 as a guide, the physician reexamines themammogram 650 to see if any of the CAD detected abnormalities suggestfurther action. The enhanced image tiles 66 and 67 provide the physicianwith further information by emphasizing the abnormal features of the CADdetected abnormalities. It is sometimes preferred that only theminiaturized annotation road map 58 be printed at the margin of themammogram 650. Alternatively, depending on the setting of a switch 73,the radiological image, annotated map and tiles can be displayed at 900in one of the ways described in connection with FIGS. 1, 2, and 3.

[0041] In order to provide an enhanced way of displaying the morerelevant information, the switch 71 is set to send the low-contrast,wide latitude radiological image and information about the suspectedabnormalities through a processor 72, that is explained in more detailin connection with FIG. 6. This processor, which can be a part of thesame programmed computer that does some of all of the processinginvolved in the embodiment of FIG. 5, uses information regarding thesuspected abnormalities that were automatically found by unit 50 toautomatically convert the low-contrast radiological image to ahigh-contrast image at the density range(s) corresponding to theabnormalities. This produces a display image that can be fed to printer580 to produce a film for display at light box 550, preferably togetherwith a display of the annotated map alone or with the tiles. Again,depending on the setting of switch 73, the display can be additionally,or instead, on a unit 900.

[0042]FIG. 6 illustrates how a CAD system in accordance with a fourthembodiment can be used to convert a low-contrast, wide-latitude digitalradiographic image to an image that has high-contrast at areas ofinterest, e.g., the areas of suspected abnormalities. One of the majorproblems in digital imaging is how to display all the informationcontained in the digitally acquired images. Typically, according to Feiget al in Volume 33 (1995) of Radiological Clinics of North America,pages 1205-30, and other sources, the exposure range of the latitude(the ratio of the exposure at the highest signal region to that at thelowest signal region) of the digitally acquired image is of the order of100 to over 1000, which is much broader than that of the display media.By comparison, if a radiogram is to be displayed on a photographic film,the exposure range of the latitude (the ratio of exposure at the highestsignal region to that at the lowest signal region where the displaygradient is significant) is of the order of 25 and the exposure range ofthe latitude of a TV monitor is less than 10.

[0043] As illustrated in FIG. 6, a CAD system 20, which can be a part ofunit 72 in FIG. 5, is used guide into two different display media thedisplay resulting from converting a low-.contrast image into ahigh-contrast image where needed, as determined by information aboutabnormalities found through processing the low-contrast image. A widelatitude digitally acquired image 800 is formatted for example such thatthe base10 log of its output signal (with an exposure range of over1000) is encoded into 12 bits (4096 levels of gray). In this example,the CAD system determines how the digital, wide-latitude radiogram 800should be printed on a photographic film 830 (having a display latitudeof, for example, 25) and displayed on a high-resolution TV or computermonitor 860 (having a display latitude of, for example, 10). Theradiogram 800 can be the digitized image 40 in FIG. 5. As illustrated inFIG. 6, this is done by centering the display latitude of the displaymedium (photographic film 830 or monitor 860) at and around the relativeexposure level of the CAD detected abnormality identified at 890 on thewide latitude image 800. That is, only the range of say the relativeexposure 10 to 100, around the CAD detected abnormality 890, say aroundrelative exposure 30, is provided at the optimum contrast gradient (sayG=3.0) while other image content, above or below the exposure range ofthe CAD detected abnormality 890, are compressed in display latitude andare displayed with reduced contrast gradient (e.g. 2.5 or less) on film830 and/or monitor 860. The monitors would normally display theprocessed x-ray images; for the purposes of illustration only, FIG. 6shows curves illustrating the relative log exposure centered around thelevel of interest, as determined by the fact that in this example asuspected abnormality has been detected at a relative log exposure of 30and gray level of 890.

[0044] Although the subject matter of this patent specification has beendescribed above in terms of preferred structures, methods and processes,it should be apparent to those skilled in the art that variousalterations and modifications can be made without departing from thescope thereof and that such modifications and alterations are intendedto be considered to be within the spirit and scope of the inventionsdefined by the appended claims.

1. A method comprising the steps of: acquiring a low-contrast,wide-latitude x-ray film image characterized by a contrast gradient G of2 or less using a medical imaging modality; converting the film image toa low-contrast, wide-latitude digital image; processing thelow-contrast, wide-latitude digital image by computer to automaticallyidentify suspected abnormalities therein; using information regardingsuspected abnormalities identified in the processing step toautomatically find a relatively narrow exposure range that includes anexposure range related to at least one of the abnormalities; convertingthe low-contrast, wide-latitude digital image to a high-contrast,narrow-latitude version display image conforming to said relativelynarrow exposure range; and displaying the display image on a displaydevice.
 2. A method as in claim 1 in which said displaying comprisesprinting said high-contrast, narrow-latitude image on photographic film.3. A method as in claim 1 in which said displaying comprises displayingsaid high-contrast, narrow-latitude image on an electronic monitor.
 4. Asystem comprising: a medical imaging unit acquiring a film image havinga relatively low contrast and relatively wide exposure rangecharacterized by a contrast gradient G of 2 or less and converting thefilm image to a low-contrast, wide latitude digital image; a programmedcomputer processing the low-contrast, wide-latitude digital image toautomatically identify suspected abnormalities therein and toautomatically find at least one relatively narrow exposure range thatincludes an exposure range related to at least one of the abnormalitiesand converting the low-contrast, wide-latitude digital image to adisplay image that is high-contrast in at least one narrow latituderelated to said at least one narrow exposure range; and a display devicefor displaying said display image.
 5. A system as in claim 4 in whichsaid display device comprises a film printer printing said display imageon photographic film.
 6. A system as in claim 4 in which said displaydevice comprises an electronic monitor.
 7. A system as in claim 4 inwhich said medical imaging unit acquires a film image having an exposurerange characterized by a contrast gradient of less than
 2. 8. A systemas in claim 4 in which the display image is characterized by a contrastgradient G of at least 3 in said narrow latitude.
 9. A system as inclaim 4 in which the display device displays a latitude exposure rangeof less than about
 25. 10. A system as in claim 4 in which: the medicalimaging unit is a mammography unit; the computer identifies suspectedspeculated lesion and microcalcification cluster type abnormalities andproduces information for an annotated map comprising symbols identifyingthe type and location of the abnormalities; and the display imageincludes the annotated map.
 11. A method comprising the steps of:producing a low-contrast, wide-latitude digital x-ray imagecharacterized by a contrast gradient G or 2 or less using a medicalimaging modality; processing the digital image by computer to identifysuspected abnormalities therein; finding, through computer processingthat does not require window and/or level selection by an operator, arelatively narrow exposure range which includes at least one exposurerange related to at least one of the abnormalities; computer-generatinga high-contrast, narrow-latitude version of said image conforming tosaid at least one relatively narrow exposure range, using informationregarding said relatively narrow exposure range provided withoutoperator intervention; and displaying said high-contrast,narrow-latitude version of said image on a display device.
 12. A methodas in claim 11 in which said displaying comprises printing saidhigh-contrast, narrow-latitude version of said image on photographicfilm.
 13. A method as in claim 11 in which said displaying comprisesdisplaying said high-contrast, narrow-latitude version of said image onan electronic monitor.
 14. A method as in claim 11 in which saidacquiring comprises acquiring a digital image that has a latitudeexposure range of more than about
 25. 15. A method as in claim 11 inwhich said acquiring comprises acquiring a digital image that has alatitude exposure range of more than about
 100. 16. A method as in claim11 in which said displaying comprises displaying an image that has alatitude exposure range of less than about
 25. 17. A system comprising:a medical imaging unit acquiring a low-contrast, wide-latitude digitalx-ray image characterized by a density gradient G no greater than 2.5; aprogrammed computer processing the digital image to automaticallyidentify suspected abnormalities therein and to find at least onerelatively narrow exposure range which includes an exposure range of atleast one of the abnormalities; said programmed computer further usinginformation regarding at least one of said abnormalities toautomatically, without requiring window and/or level selection by anoperator, convert the digital image to a high-contrast, narrow latitudedisplay image that includes said at least one relatively narrow exposurerange; and a display device for displaying said display image.
 18. Asystem as in claim 17 in which said display device comprises a filmprinter printing said display image on photographic film.
 19. A systemas in claim 17 in which said display device comprises an electronicmonitor displaying said display image.
 20. A system as in claim 17 inwhich: the medical imaging unit is a mammography unit; the computeridentifies suspected speculated lesion and microcalcification clustertype abnormalities and produces information for an annotated mapcomprising symbols identifying the type and location of theabnormalities; said display image comprises a mammogram; and the displaydevice displays the annotated map in addition to displaying saidmammogram.
 21. A method comprising: imaging a breast with x-rays toproduce an initial image characterized by a contrast gradient G nogreater than 2.5; processing the initial image with a programmedcomputer to identify suspected abnormalities; using informationresulting from the processing step to identify a latitude narrower thanthat of the initial image; converting the initial image to a displayimage characterized by a density gradient G or at least 3 within saidnarrower latitude; and displaying the display image.
 22. A method as inclaim 21 in which the processing step includes generating an annotatedmap of said abnormalities, and the displaying step comprises displayingsaid map as a part of or adjacent said display image.
 23. A method as inclaim 17 in which said imaging comprises imaging at KVp in the range of40-55.